Conventionally, a variety of methods has been used to bond metal members to each other. According to Non-Patent Document 1, the metal bonding method is generally sorted into a metallic bonding method, a chemical bonding method and a physical bonding method. Any one of these bonding methods has been used to bond aluminum alloy materials to each other.
The metallic bonding method is to strongly bond metal members to each other. By suitably carrying out the metallic bonding method, it is possible to enhance high reliability in the bond junction of the metal members. Concretely, the metallic bonding method is further sorted into a metal-fusing/welding type bonding method; a solid-phase type bonding method such as a diffusion bonding method, a friction bonding method, a pressure bonding method and so forth; and a liquid-phase/solid-phase reaction type bonding method such as a brazing method and so forth. Especially, in the brazing method, which is defined as the liquid-phase/solid-phase reaction type bonding method, since a bonding process is carried out by heating a whole of metal members to be bonded in an furnace, it is possible to simultaneously bond the metal members at plural locations. The brazing method featuring this technical advantage is mostly applied to manufacture of a product, having many bonding locations in a narrow space, such as a heat exchanger for an automobile, a heat sink and so forth.
The chemical bonding method is defined as one using an adhesive. This chemical bonding method is different from the metallic bonding method in that it is unnecessary to carry out a bonding process at a high temperature, and thus features a technical advantage that metal members to be bonded are subjected to thermal deformation. Nevertheless, in the chemical bonding method, since it is impossible to obtain a strong bonding force like the metallic bonds, there are disadvantages that reliability and thermal conductivity in the bond junction of the metal members are inferior to the metallic bonding method.
The physical bonding method is defined as one using rivets, bolts and so forth. In this physical bonding method, a bonding process can be easily carried out with comparison with the metallic bonding method and the chemical bonding method. Also, it is possible to obtain a bonding strength which is equivalent to or more than that of the metallic bonding method. Nevertheless, there are disadvantages that a configuration in the bond junction of metal members to be bonded is limited, and that the physical bonding method is unsuitable when tightness is needed in the bond junction of the metal members.
Conventionally, in order to bond aluminum alloy materials to each other, a metallic bonding method such as a welding method, a soldering method, a brazing method and so forth has been used.
In the welding method, portions of aluminum alloy members to be bonded are heated and melted by using electricity or flame, to thereby alloy the portions with each other, resulting in the portions of the aluminum alloy members being bonded to each other. When a clearance between the portions of the aluminum alloy members is large or when a sufficient bonding strength is needed, a filler material is simultaneously melted during the bonding process so that the clearance is filled with the melted filler material. In this welding method, since the portions of the aluminum alloy members to be bonded are melted, it is possible to securely bond the portions of the aluminum alloy members to each other. Nevertheless, due to the fact that the portions of the aluminum alloy members are melted and bonded to each other, the aluminum alloy members may be largely deformed in the vicinity of the portions thereof to be bonded, and the melted portions may locally and largely change from the original metal structure into another metal structure, so that the bonded portions may be locally weakened. Also, due to the fact that only the portions of the aluminum alloy members to be bonded must be heated during the bonding process, there is a problem that it is very difficult to simultaneously bond the aluminum alloy members at plural locations.
In the soldering method or the brazing method, a soldering material or a brazing material is used, and has a melting point lower than those of aluminum alloy members to be bonded. Thus, only the soldering material or the brazing material is heated and melted by using electricity or flame, so that the melted soldering or brazing material is filled with a clearance between portions of aluminum alloy members to be bonded, resulting in the portions of the aluminum alloy members being bonded to each other. When the portions of the aluminum alloy members have a spot-like configuration or a linear-like configuration, it is possible to advantageously bond them to each other, and, by defining a so-called fillet during solidification of the melted soldering or brazing material, it is possible to obtain high reliability on strength, thermal conductivity and so forth in the bond junction of the aluminum alloy members. Also, the portions of the aluminum alloy members can be firmly bonded to each other in a short time without melting the base materials thereof. Especially, a furnace-type brazing method such as a NOCOLOK brazing method, a vacuum brazing method and so forth features a brazing sheet which is composed of an aluminum alloy material defining a member to be bonded, and a brazing material cladded on the member to be bonded. After brazing sheets are pressed and are formed into a lamination type heat exchanger assembly having a hollow structure, by merely heating it in a furnace, it is possible to manufacture a heat exchanger featuring many bonding locations and complex configurations. Nevertheless, in the furnace-type brazing method, the melted liquid-phase soldering or brazing material easily flows over so that small passages in the heat exchanger may be filled with the melted soldering or brazing material. Also, when brazing sheets are used, there is an advantage that the melted soldering or brazing material can be uniformly given to portions of aluminum alloy members to be bonded. Nevertheless, due to the fact that the manufacture of a brazing sheet is complex, there are demands that the brazing sheet should be manufactured at small cost, and that supply of the brazing sheet should be improved. Further, there are problems that a degree of freedom on a machine work such as a cutting and so forth, to which faces of aluminum alloy members to be bonded should be subjected, is reduced.
As a general rule, the solid-phase type bonding method such as the diffusion bonding method, the friction bonding method and so forth is defined as one in which melt of metal members to be bonded is not involved.
Basically, the diffusion bonding method is defined as one in which base metal materials are closely pressed against each other at a temperature lower than a melting point of the base metal materials without being subjected to plastic deformation, resulting in the metal materials being bonded to each other due to atom diffusion caused in a boundary between the faces to be bonded in the base metal materials. According to this bonding method, it is possible to simultaneously bond the base metal materials at plural locations or in plural faces without being to plastic deformation. Thus, metal members having fine configurations can be even bonded to each other. Nevertheless, due to the fact that the diffusion phenomenon is utilized, a bonding process needs longer time in comparison with the welding method, the brazing method and so forth. Usually, it is necessary to hold the metal members to be bonded at a given temperature over a time period of about 30 minutes or more than 30 minutes. Also, due to the fact that the bonding process involves pressurization, a bonding operation is troublesome, resulting in an increase in cost of the bonding process. Further, when each of the metal members to be bonded is composed of an aluminum alloy material, it is difficult to carry out the solid-phase diffusion bonding method due to the fact that the diffusion is hindered by a stable and firm oxide film existing over a surface of the aluminum alloy material. When each of the metal members to be bonded is composed of an aluminum alloy material which contains Mg falling within a range of about 0.5-1.0 mass %, it is possible to relatively easily carry out the bonding process because the oxide film can be demolished due to reduction of Mg. However, in other aluminum alloy materials, there is a problem that a specific cleaning process such as an argon ion bombardment cleaning process, a glow discharge cleaning process, a supersonic cleaning process and so forth is needed to remove the oxide film from an aluminum alloy material.
A friction stir bonding method, which is included in the friction bonding method, can be applied to all of the aluminum alloy materials. Due to the fact that the friction stir bonding method involves no melt of a base material, there is an advantage that members to be bonded to each other are not nearly subjected to deformation during a bonding process. Nevertheless, the members to be bonded to each other are limited to a linear configuration or a loose curved configuration, and it is difficult to bond members having a complicated configuration to each other. Also, due to the fact that a bonding tool is directly contacted with the members to be bonded, not only it is difficult to bond the members having fine configurations to each other, but also it is difficult to simultaneously bond the members at plural locations. Also, in this bonding method, it is impossible to avoid the remainder of a bonding pin mark on terminal ends of the members to be bonded to each other. Further, due to the fact that the members to be bonded to each other are stirred at the bond junction, a structure at the bond junction is different from that of the base material, and thus there is a problem that a bonding strength may be deteriorated.
As stated above, when members composed of aluminum materials are bonded to each other by the metallic bonding method, in general, the bonding methods, in which the members to be bonded are not melted or in which only the portions of the members to be bonded are locally melted, have been adopted as the metallic bonding method. This is because a desirable configuration cannot be obtained when the members to be bonded are wholly melted. Nevertheless, before a bonding process can be carried out at a practical rate, it is necessary to partially melt the members to be bonded, and thus deformation on the melted portions cannot be avoided. Therefore, there is a problem that design and assembly on the members to be bonded must be carried out, in anticipation of dimensional change and strength change to which the bonded members should be subjected after the bonding process.
On the other hand, a bonding method, which is carried out in a semi-melting state of metal members, has been proposed. In Patent Document 1, a bonding method utilizing a semi-melt state of alloy powder is proposed. In this bonding method, since alloy powders, which are defined as members to be bonded, are wholly in a semi-melt state, configurations of the members to be bonded are remarkably deformed, and thus the bonding method is unsuitable for a case where it is desired that the deformation of the members to be bonded is suppressed during a bonding process. Also, in Patent Document 2, is proposed a bonding method in which a nonmetallic member and a base alloy material are bonded to each other by pressing the nonmetallic member into the base alloy material in a semi-melting state. Nevertheless, in this bonding method, since the bonding is carried out with the use of a punch and a metal die, the resulting configuration of a product is limited.
Also, in Patent Document 3, is proposed a diffusion bonding method which is used to manufacture a waveguide antenna, and in which a slot plate forming a waveguide and a substrate composed of an Mg-based aluminum alloy are bonded by heating and exerting a pressure on them at a temperature which falls within a solid-liquid coexisting region of the aluminum alloy or which is in the vicinity of the solid-liquid coexisting region thereof. In the diffusion bonding method, the faces to be bonded to each other are pressurized by a tool using a wedge, and are further pressurized by utilizing a thermal expansion difference between the tool and the aluminum alloy, to thereby carry out the diffusion bond of the slot plate and the substrate. In this case, Patent Document 3 discloses that a liquid-phase ratio in the slot plate and the substrate is 1.7% at maximum as a bonding condition. Nevertheless, when the liquid-phase ratio is about 1.7%, an amount of a liquid phase material to be produced is too small, and thus there may be a case where the slot plate and the substrate cannot be bonded to each other at a sufficient strength. Also, in the method proposed by Patent Document 3, when the temperature is further elevated so that the liquid-phase ratio is increased, there may be case where a pressure exerted on the slot plate and the substrate is too much so that they are subjected to large deformation. Further, in this method, it is possible to bond only flat plate-like members to each other, and an orientation of the faces to be bonded is limited to the pressurizing direction.
In Patent Document 4, is proposed a method in which two members composed of respective metal alloys are received in a forging die, and in which a shaping and a bonding the two members are simultaneously carried out at a temperature which is set so that a solid-phase ratio of the two members falls within a range from 30% to less than 90% (a liquid-phase ratio thereof falling within a range from 10% to less than 70%). Since this method is to produce a composite material from the two members, it is impossible to bond the two members to each other so that configurations of the members before and after the bonding are maintained. Also, in this method, it is impossible to define a hollow between the two members to be bonded, and non-flat members cannot be bonded to each other. Further, in this method, a large-scale and high-temperature forging machine is needed.